For many reactions it is desirable to supply the starting components to the reaction zone in a distribution which is as uniform as possible, particularly if the reaction is to be effected in the presence of a catalyst. For this reason the previous practice has been to mix the starting components at a considerable distance from the reaction zone so that the desired homogeneity of the mixture is ensured by the mixing means and by an adequate residence time in the path leading to the reactor.
For certain reactions, such as the oxidation of orthoxylene or naphthalene with air to form phthalic anhydride, a large quantity of energy is usually required to pressurize the mixture to the pressure required in the reaction zone. For this reason it is desirable to increase the loading of the gas with the finely divided liquid so that the overall energy balance of the process will be improved. But a uniform distribution of the liquid in the gas cannot easily be achieved.